1. Field of the Invention
The present invention relates to the forming of a camshaft by binding the cams on a tube by expanding the tube. It more specifically relates to a device for holding the cams during the binding.
2. Discussion of the Related Art
FIG. 1 schematically illustrates cam being secured on a tube such as described, for example, in U.S. Pat. No. 4,597,365. Several cam 10 are arranged around a tube 12 that initially engages with a slight play in bores of cam 10. Cams 10 are held at desired axial and angular positions by a holding device not shown in FIG. 1.
A tube expander 14 is engaged in tube 12, and its diameter is such that the external diameter of tube 12 is enlarged to become slightly greater than the internal diameter of cams 10. This results, as shown in the left-hand portion of FIG. 1, in a permanent deformation of the tube and a binding thereof in the bores of cams 10.
In the above-mentioned U.S. patent, cams 10 are forged steel cams, the angular position of which is ensured by V shaped holders. The cam manufacturing precision being insufficient, it is necessary to rectify the cams after their binding on the tube, to restore the required dimensions.
The applicant has used this assembly technique for sintered cams. Sintered cams are generally made with a precision such that a rectification could be omitted if they were properly positioned during the binding.
FIG. 2 illustrates a front view of a sintered cam arranged in a holding device such as used by the applicant. For each cam 10, an upper block 16 and a lower block 17 intended for accomodating cam 10 and holding its angular position during the binding are provided. They are further used to avoid the breaking of the cam during the binding.
In blocks 16 and 17, housings corresponding to the contour of cam 10 have been precisely worked, by choosing for these housings the maximum dimensions of the cam manufacturing tolerance range. As shown, a play is provided between blocks 16 and 17, on either side of the cam, so that the housings of these cams always bear with no play on the circumference of cam 10.
With this configuration, it has been expected to ensure a faultless positioning of cam 10 while preventing the cam from breaking during the binding. Indeed, sintered cams are less resistant than cams obtained by other methods and risk cracking during the binding if they are not held along their entire circumference.
Upper blocks 16 and lower blocks 17 are attached side by side along the tube, for example by bolts that run through holes 19 of the cams. Two half-cases that are firmly held against each other, for example, by means of a press, during the binding are thus formed.
Despite these precautions, some cams still appear to have a bad angular position and must be rectified.
An object of the present invention is to provide a device for holding the cams during their binding on a tube, which enables obtaining a camshaft that requires no rectification.
To achieve this object, the present invention provides a device for holding sintered cams during their binding on a tube by expansion of the tube, including, for each cam, two blocks intended for enclosing the cam in housings complementary to the cam contour. The dimensions of the housings are chosen so that the play between the housings and the largest cam in a predetermined tolerance range is as close to zero as possible by excess, the two blocks being provided to bear against each other whatever the dimensions of the cam within the tolerance range.
According to an embodiment of the present invention, the device includes means for preventing a play from appearing between the two blocks associated with a cam during the tube expansion.
According to an embodiment of the present invention, several blocks are assembled side by side along the tube, forming two half-cases, the two half-cases being held against each other during the tube expansion by several independent jacks, distributed on a surface of one of the half-cases.
The foregoing objects, features and advantages of the present invention, will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings.